Issue 5013 - Make parameter const ref when applicable.

test/FileSystemJsObject.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 32 matching lines @@
 
     std::shared_ptr<std::istream> Read(const std::string& path) const
     {
       if (!success)
         throw std::runtime_error("Unable to read " + path);
       std::stringstream* const stream = new std::stringstream;
       *stream << contentToRead;
       return std::shared_ptr<std::istream>(stream);
     }
 
-    void Write(const std::string& path, const std::istream& data)
+    void Write(const std::string& path, std::istream& data)
     {
       if (!success)
         throw std::runtime_error("Unable to write to " + path);
       lastWrittenPath = path;
 
       std::stringstream content;
       content << data.rdbuf();
       lastWrittenContent = content.str();
     }
 
@@ skipping 175 matching lines @@
   ASSERT_ANY_THROW(jsEngine->Evaluate("_fileSystem.stat('', '')"));
 }
 
 TEST_F(FileSystemJsObjectTest, StatError)
 {
   mockFileSystem->success = false;
   jsEngine->Evaluate("_fileSystem.stat('foo', function(r) {result = r})");
   AdblockPlus::Sleep(50);
   ASSERT_NE("", jsEngine->Evaluate("result.error")->AsString());
 }